This mod is so absurdly fun to explore!
The mechanics of Encore mode are used very well in the familiar sections of the levels, and especially in some of the unfamiliar sections of the levels! These stages reward you generously for your knowledge of the levels from the original game. Despite getting my ass kicked by the last two special stages multiple times, by the time I got to CE3 (or ACZ1 since emeralds don't matter in boss levels) I already had all the Chaos Emeralds just due to the sheer amount of tokens you get for looking around in familiar locations. Some can be found in the same place as usual, such as the one behind the door in DSZ1 and the spring-gauntlet one in CEZ1, but a lot are in areas you'll hopefully remember to look if you've gone hunting for those more secret emblems and extra lives.
My complaints are mostly parrots of some earlier reviews, mainly Special Stage 7's time limit and the small amount of i-frames when respawning as your partner character. Magma Caves can be cleared with some good time management and movement, including slipping right between that last mine and the cannon to make sure you don't lose those 5 seconds and hitting that super paraloop a little safer and earlier than usual, but Egg Satellite pretty much requires a perfect run to hit it. You're pretty much done if you don't hit the laser room paraloop where the Sun Emblem usually is, considering you'll probably end up with just barely under the requirement when you get to the capsule even if you hit everything else perfectly. This on top of the fact two mistakes pretty much means you're dead makes this stage especially brutal. Just another 10 seconds would help this level a lot, not removing it's brutality but giving you just a bit more room to breathe. As for the other issue, I didn't experience it much, but it becomes apparent when you land in the thorns in CEZ3 due to Tangle not being able to hit Eggman even on the edge and then immediately losing three characters to the thorns. There are some i-frames, but just not enough to escape without immediate action.
Those are my only gripes, and they're very easy to look past when compared to the rest of my experience! To the throwbacks to older versions in Egg Rock to the more interesting boss arenas (some of which are also throwbacks) to not making that ungodly final section in ACZ1 more difficult than it needs to be, you're gonna have a lot of fun if you're an experienced player of this game! As of the time of writing, admittedly, I haven't beat Encore Mode, because the Metal Sonic race is so damn tight that I decided to call it a night after an hour of attempts and I'll have to do another playthrough to get another shot at him. Here's to finally beating that bastard and seeing what comes after!